A. Field of the Invention
This invention relates to the field of data communication. More particularly, the invention relates to transmission profiles that are assigned to individual modems in an upstream direction, on a modem by modem basis, to optimize their transmission in the upstream direction in order to maximize throughput. The invention is applicable to both wireless and land-based communications systems, particularly those adhering to the Data-Over-Cable Service Interface Specifications (“DOCSIS”)—Radio Frequency Interface Specification standard, or other standards which are analogous to the DOCSIS standard.
B. Description of Related Art
With the explosive growth of the Internet, many customers have desired to use the larger bandwidth of a cable television network to connect to the Internet and other computer networks. Cable modems, such as those provided by 3Com Corporation of Santa Clara, Calif., and others offer customers higher-speed connectivity to the Internet, an intranet, local area networks (“LANs”), and other computer networks via cable television networks. These cable modems currently support a data connection to the Internet and other computer networks via a cable television network with a data rate of up to 30+Mbps, which is a much larger data rate than can be supported by a modem used over a standard telephone line. Background information related to cable modem systems in general is described in the Data-Over-Cable Service Interface Specifications (“DOCSIS”)—Radio Frequency Interface Specifications, issued by Cable Television Laboratories, Inc. This document, known to persons working in the art, is incorporated by reference herein in its entirety.
Data-over-cable systems may serve many cable modems simultaneously. A cable modem receives and transmits data in the form of digitally encoded radio frequency transmissions, which typically travel to and from the cable modem on, for example, coaxial cable. Also, the data-over-cable system consists of many branches from a common trunk, each branch serving a distinct group of cable modems, and the branches themselves may further divide into sub-branches. Thus the propagation of radio frequency signals to and from the cable modem often follows a circuitous and convoluted path. Transmissions from the cable modem are terminated in a cable system head-end by a device known as a Cable Modem Termination System or CMTS.
The current DOCSIS specification uses two types of message structures to describe when and in what manner a cable modem can transmit information on an upstream channel, i.e., in the direction from the cable modem to the CMTS. They are an Upstream Channel Descriptor (UCD) and an Upstream Bandwidth Allocation Map (MAP).
The UCD specifies the transmission characteristics of a given upstream channel. In particular, it specifies two aspects of an upstream transmission: channel specific items and burst specific items. Channel specific items or parameters are those that are common to all bursts of data, such as the operating frequency, the symbol rate, and the preamble pattern. Burst parameters, on the other hand, are specific to a given burst type, and include such characteristics as the modulation type, error correction parameters, and burst size. DOCSIS defines burst types by the purpose of the upstream transmission. These purposes are defined by a set of codes, known as Interval Usage Codes (IUC). The defined usage codes include “Requests”, “Requests/Data”, “Initial Maintenance”, “Station Maintenance”, “Short Data Grant”, “Long Data Grant”, and “Data Acknowledgment.”
While UCDs thus describe the transmission characteristics of the channel, the MAP message structure defines the timing and control of the actual upstream data transmission. The MAP message structure includes one or more information elements (IE) fields, each of which defines a burst of transmission. Each IE within the MAP defines what modem or modems can transmit (through a service identifier), what type of transmission is allowed (via the IUC), and how long the transmission interval is.
The DOCSIS system is limited in its applicability to other transmission media besides cable because it defines transmission by the type of transmission only. DOCSIS assumes a channel has common transmission characteristics for all modems. It lacks the capability to also define transmission based on the quality of an individual upstream transmission path. That is, it does not readily enable adaptive modulation, namely the varying of the upstream transmission characteristics on a burst by burst and modem by modem basis in response to the current channel conditions. This situation prevents the maximization of upstream transmission on a per modem basis, since DOCSIS systems must be configured to support the lowest performing link.
For example, assume that modem A has a bad upstream transmission path, while modem B has a clean transmission path (while not probable in a wired environment, it is highly probably in a wireless environment). Because the UCD under the current DOCSIS regime only allows one transmission characteristic definition for a particular transmission type, all modems, regardless of the link quality, must use the same transmission format. Because modem B has a cleaner path, it could transmit data at a higher rate than modem A. However, because of the way the UCD is defined, it must use the same data rate as modem A. Since it is not practical to change the UCD from burst to burst (since it wastes downstream bandwidth, and the modem must continually process new UCD characteristics), this remains a limitation. Alternatively, additional IUCs could be created, but their basic function of defining the transmission type is still needed.
The present invention solves this problem by recognizing that the UCD and MAP format can be modified to specify upstream transmission characteristics on a burst by burst and modem by modem basis. This can be achieved by having the UCD define “transmission profiles.” The profiles, as explained below, are a set of defined transmission parameters. One of the profiles is assigned to the modem, hence it tells the modem how to configure itself in an optimum and individual fashion, independent of other modems. The UCD thus defines profiles, instead of channel and burst characteristics, and the MAP IEs include profile assignments as is described below. This feature makes the DOCSIS message scheme extensible to other transmission media besides cable, particularly those where transmission characteristics and transmission parameters vary, such as wireless.